Principles of Infection

Question 1

Term describing where microbes take up permanent residence but don’t cause disease under “normal” circumstances

Answer 1

Normal flora

Question 2

Term where microbes colonise for a brief time and may cause disease, but normal flora competes and it doesn’t last

Answer 2

Transient flora

Question 3

Term where disease causing microbes cause an infection

Answer 3

Pathogenic flora

Question 4

What factors need to be in place for microbes to cause disease (the balancing act)?

Answer 4

Factors of the MICROBE, HOST and ENVIRONMENT all contribute to the manifestation of disease

Question 5

What is is about a microbe that makes them pathogenic?

Answer 5

The ability to cause disease (depends on virulence, susceptible host and conducive environment)

Question 6

What is symbiosis?

Answer 6

Living things living together

Question 7

The 4 possible outcomes of symbiosis

Answer 7

1. Mutualism (mutual benefit)
2. Commensalism (benefit is one way, but no harm done)
3. Parasitism (one lives at the expense of the other)
4. Opportunism (under normal conditions, commensal, but when host is compromised, harm is done)

Question 8

What is an example of mutualism?

Answer 8

The mutual benefit of Lactobacillus acidophilus in the adult vagina - maintains acid pH (4), providing protection

Question 9

What is an example of commensalism?

Answer 9

The one way benefit/no harm or Staphylococcus epidermidis on the skin - under normal circumstances doesn’t cause harm

Question 10

What is the term for all pathogenic microbes that live at the expense of others?

Answer 10

Parasitism

Question 11

What is an example of opportunism?

Answer 11

Candida albicans (thrush) - lives in normal flora, but can increase and establish infection under certain conditions

Question 12

To be considered a pathogen, what are the 4 things a microbe must be able to do?

Answer 12

1. Gain entry to a host
2. Attach and multiply
3. Evade host defences
4. Cause damage to tissues

Question 13

Give examples of ‘signs’ of disease. What determines a sign, as opposed to a symptom?

Answer 13

• High temperature
• Skin changes
• Blood cells involved in host defences increase

SIGNS ARE MEASURABLE

Question 14

Give examples of ‘symptoms’ of disease. What determines a symptom, as opposed to a sign?

Answer 14

• Pain (headache)
• Nausea
• Malaise

SYMPTOMS ARE NOT MEASURABLE

Question 15

The first phase of infection is i________

Answer 15

Incubation (no signs or symptoms)

Question 16

The second phase of infection is the p________ p_____

Answer 16

Prodromal phase (mild signs and symptoms)

Question 17

The third phase of infection is the a_____ p_____

Answer 17

Acute phase (acute identifiable disease symptoms)

Question 18

Once the acute phase of infection has been reached, there will be one of which two outcomes to follow?

Answer 18

Decline of organisms OR Death

Question 19

The final phase of infection is c__________

Answer 19

Convalescence